1. Field of the Invention
The present invention relates to an electric automobile driving apparatus for driving the motor by converting the DC voltage supplied to the main battery into an alternating current and, more particularly, to an electric automobile driving apparatus provided with an auxiliary battery for supplying a DC voltage to the electric appliances installed in the automobile.
2. Description of the Related Art
FIG. 8 shows an example of a conventional electric automobile driving apparatus.
In FIG. 8, an electric automobile driving apparatus installed in an electric automobile 10 includes a main battery 12 for outputting a DC voltage, a power converter 14 for converting the DC voltage output from the main battery 12 into alternating currents of three phases I.sub.U, I.sub.V, I.sub.W, and a motor 16 which is driven by the alternating currents I.sub.U, I.sub.V, I.sub.W.
The DC voltage output from the battery 12 is converted into the alternating currents I.sub.U, I.sub.V, I.sub.W by the power converter 14 which is constituted by, for example, an inverter.
The alternating currents I.sub.U, I.sub.V, I.sub.W are supplied to the primary coil of the motor 16. In the motor 16, the alternating currents I.sub.U, I.sub.V, I.sub.W are converted into an alternating field, thereby producing a rotational driving force. The rotational driving force is supplied to for example, a rear wheel 18 through an axle. In this way, the electric automobile 10 is driven.
To the main battery 12, a DC-DC converter 20 is connected which converts the DC voltage output from the main battery 12 into a DC voltage having a different value.
An auxiliary battery 22 for supplying a DC voltage to the electric appliances installed in the automobile is connected to the DC-DC converter 20.
The DC voltage output from the main battery 12 is converted into a DC voltage having a different value (e.g., 12 V) by the DC-DC converter 20, and the auxiliary battery 22 is charged with the converted DC voltage. The auxiliary battery 22 is a battery for driving the electric appliances installed in the automobile such as a lamp and a wiper. It is generally necessary that these electric appliances installed in the automobile are driven by a voltage having a different value from the DC voltage output from the main battery 12 so as to drive the motor 16. Therefore, the auxiliary battery 22 is charged with a DC voltage having a different value from that output from the main battery 12, and outputs a voltage to the electric appliances installed in the automobile, if necessary.
The conventional electric automobile driving apparatus is provided with a control unit 24 for controlling the power converter 14. A pulse generator 26 for detecting the number of revolutions .omega..sub.r of the motor 16 is connected to the control unit 24 and the information on the alternating currents I.sub.U, I.sub.V, I.sub.W is input from the pulse generator 26 to the control unit 24.
FIG. 9 shows the structure of the power converter 14 which is controlled by the control unit 24.
In FIG. 9, the power converter 14 is provided with two transistors connected in series to each other and two diodes connected in series to each other in correspondence to each of the phases U, V and W of the motor 16. Both ends of these two transistors connected in series to each other and two diodes connected in series to each other are connected to the main battery 12, and the connecting points of the direct connection thereof are connected to the corresponding phases of the motor 16.
In the motor 16, the output end of the power converter 14 is connected to one end of a primary coil 30 disposed on a stator 28. In FIG. 9, the primary coils 30U, 30V and 30W of the respective phases are connected to each other in a Y-connection.
The power converter 14 shown in FIG. 9 is controlled by a control signal supplied from the control unit 24.
For example, a control signal U.sub.P output from the control unit 24 is supplied to the base of the transistor which is connected to the positive side of the main battery 12 in correspondence with the U-phase of the motor 16 and, similarly, a control signal U.sub.N output from the control unit 24 is supplied to the base of the transistor which is connected to the negative side of the main battery 12 in correspondence with the U-phase of the motor 16.
The ON/OFF of the transistors are controlled by these control signals U.sub.P and U.sub.N. Similarly, the ON/OFF of the transistors corresponding to the V-phase are controlled by control signals V.sub.P and V.sub.N and the ON/OFF of the transistors corresponding to the W-phase are controlled by control signals W.sub.P and W.sub.N. If such ON/OFF control is carried out such that the DC currents I.sub.U, I.sub.V, I.sub.W supplied to the respective U-, V- and W-phases alternate, an alternating field is produced within the motor 16 and a rotor 32 is rotated by the alternating field.
FIG. 10 shows the structure of the control unit 24 for controlling the current of the power converter 14.
In FIG. 10, the control unit 24 is composed of a command operation circuit 32 for calculating the desired values I.sub.UO, I.sub.VO and I.sub.WO of the alternating currents I.sub.U, I.sub.V and I.sub.W on the basis of the number of revolutions .omega..sub.r of the motor 16 and a control signal generator 34 for outputting the control signals U.sub.P, U.sub.N, V.sub.P, V.sub.N, W.sub.P and W.sub.N on the basis of the desired values I.sub.UO, I.sub.VO and I.sub.WO. The control signal generator 34 is composed of a triangular wave generator 36 for generating a triangular wave having a predetermined frequency, an operational amplifier 38 for outputting a PWM pulse signal, a constant-voltage diode 40 connected to the output end of the operational amplifier 38, and an NOT 42 for inverting the pulse signal supplied through the constant-voltage diode 40.
When the number of revolutions .omega..sub.r of the motor 16 is detected by the pulse generator 26, the desired values I.sub.UO, I.sub.VO and I.sub.WO are calculated and determined by the command operation circuit desired values I.sub.UO, I.sub.VO and I.sub.WO are input to the operational amplifiers 38U, 38V and 38W, respectively.
To the operational amplifiers 38U, 38V and 38W are input the signals representing the actual alternating currents I.sub.U, I.sub.V and I.sub.W, respectively, and further the triangular wave output from the triangle wave generator 36. The operational amplifiers 38U, 38V and 38W output pulse voltages subjected to PWM in correspondence with the difference between the desired values and the actual alternating currents as the control signals U.sub.P, V.sub.P and W.sub.P, respectively. These control signals U.sub.P, V.sub.P and W.sub.P are inverted by the NOT's 42U, 42V and 42W, respectively, and output as the control signals U.sub.N, V.sub.N and W.sub.N, respectively.
FIG. 11 shows the structure of the DC-DC converter 20.
In FIG. 11, the DC-DC converter is composed of a DC/AC converter 44 for converting the DC voltage supplied from the main battery 12 into an AC voltage, a transformer 46 for transforming the AC voltage output from the DC/AC converter 44, and a rectifier 48 for rectifying the output of the transformer 46.
The rectifier 48 is connected to the auxiliary battery 22. The DC voltage output from the main battery 12 is converted into an AC voltage by the DC/AC converter 44, and transformed by the transformer 46. The AC voltage output from the transformer 46 is rectified by the control unit 48 but the DC voltage obtained as a result of the rectification has a different value from that of the DC voltage output from the main battery 12. For example, if the DC voltage output from the main battery is 100 V, the DC voltage supplied to the auxiliary battery 22 is set at 12 V. The auxiliary battery 22 is charged with the DC voltage output from the rectifier 48 and outputs the rectified DC voltage to electric appliances installed in the automobile.
FIG. 12 shows another example of the structure of a conventional electric automobile driving apparatus.
This example is the same as that disclosed in, for example, Japanese Utility Model Laid-Open No. 111827 (1973). In FIG. 12, the DC-DC converter 20 is only shown.
The rectifier 48 in this example includes a relay 50 which is turned on/off by the output voltage of the transformer 46.
In the first and second examples of the conventional electric automobile driving apparatus, the DC voltage output from the main battery 12 is converted into the alternating currents I.sub.U, I.sub.V and I.sub.W, and the motor 16 is driven by the alternating currents I.sub.U, I.sub.V and I.sub.W.
The DC voltage output from the main battery 12 is converted into a DC voltage having a different value by the DC-DC converter 20, and the auxiliary battery 22 is charged with the converted voltage.
In this way, the electric automobile 10 is driven and the electric appliances installed in the electric automobile 10 are operated by the DC voltage supplied from the auxiliary battery 22.
The conventional electric automobile driving apparatus having the above-described structure, however, has some problems in design, cost, reliability, etc. because the DC-DC converter for charging the auxiliary battery is necessary, thereby making the structure complicated. In addition, the DC-DC converter includes a transformer which generally has a large weight, thereby suffering from the problem of the large weight of an electric automobile.